Mexico has confirmed 11 pregnant women are infected with the Zika virus, out of a total of 121 cases, the government said on Monday.

Most of the cases were identified in the southern Mexican states of Chiapas and Oaxaca, according to a health ministry report.

Eight of the pregnant women are from Chiapas, two are from Oaxaca, and one is from the Gulf coast state of Veracruz, the health ministry reported.

The number of cases of infected pregnant women has risen since mid-February, when the health ministry said there were 80 confirmed cases of Zika, including six cases of pregnant women with the virus.

Much remains unknown about Zika, including whether the virus actually causes microcephaly, a condition marked by unusually small heads that can result in developmental problems.

Brazil said it has confirmed more than 580 cases of microcephaly, and considers most of them to be related to Zika infections in the mothers. Brazil is investigating more than 4,100 additional suspected cases of microcephaly.